The present invention relates to display backlighting systems. More particularly, the present invention relates to a cold cathode fluorescent lamp backlighting system providing an expanded dimming range.
Liquid crystal displays (LCDs) are frequently used as display devices in aircraft. To accommodate low level night operation and high ambient sunlight conditions, an extremely large backlight dimming range is typically necessary. A desired dynamic luminance range ratio of 3000:1 (the ratio of the highest luminance output to the lowest possible luminance output) or more is highly desirable.
Cold cathode fluorescent lamp technology has long been a source of lighting for the laptop personal computer (PC) industry which requires long life, efficient operation, an inexpensive cost structure, but only limited dimability. The fact that these lamps are difficult to dim over more than a range of 500:1 has precluded their usage in most aviation electronics (avionics) applications which require significantly more dynamic luminance range. While some avionics manufacturers have been successful in putting cold cathode lamps in flight deck applications, the dimming performance (typically no greater than 1000:1) has precluded their application to a primary flight display on which critical pilot information is provided.
A method of backlighting a flat panel display over an expanded dimming range includes providing a backlight including multiple cold cathode fluorescent lamps positionable directly behind a diffuser. Each of multiple drive circuits is adapted to independently adjust arc current of at least one of the multiple cold cathode fluorescent lamps in order to change the luminance output of the at least one of the cold cathode fluorescent lamps. Control signals are provided to each of the multiple drive circuits to separately control luminance output of different cold cathode fluorescent lamps such that at the same instant the different cold cathode fluorescent lamps are driven to substantially different luminance intensities, thereby allowing a reduction of an overall minimum luminance provided by the backlight and expanding the dimmable range of the backlight. A backlight implementing the methods of the invention is also disclosed.